DUBLIN - Twenty-three people were sickened Tuesday morning by what officials suspect is an overdose of fluoride in the drinking water at a Dublin business.

Half of those made ill complained of acute symptoms, including stomach pains and vomiting. Three people were taken to a hospital, said Bert Michalczyk, the Dublin-San Ramon Services District general manager.

The victims were employees of Humphrey Systems Inc., an optical goods company on Hacienda Drive in Eastern Dublin.

About 11 a.m. several people began to feel ill, and company officials quickly discovered that all of them drank from water fountains, Michalczyk said.

"We went out to the facility and asked them to turn on all the faucets to flush out any fluoride. We're emptying the system of its bad water and bringing in the good water," he said.

District crews also disconnected the pump that injects fluoride into the area's water supply as the eastern Dublin system was being flushed clean. No other people in the area complained of illness Tuesday.

The Alameda County health department and the police department were notified, although no foul play is suspected, Michalczyk said.

He said a malfunctioning fluoride pump might be to blame, although no final cause had been determined Tuesday evening.

The district tries to maintain a fluoride level of about one milligram per liter in the drinking supply. Tests at Humphrey Systems on Tuesday showed concentrations of up to 200 milligrams per liter.

Tuesday's incident was not the first time DSRSD had problems with its fluoride program. Dublin went without fluoride in its drinking water for about five months last year because of problems with the delivery system.

Also, the pump suspected to have malfunctioned Tuesday stopped injecting fluoride into the water briefly after it was installed last spring.